[REQ] "throws Exception" for specified APIs

Is your feature request related to a problem? Please describe.

we have api.yaml definition

openapi: "3.0.2"
info:
  version: "1.0.0"
  title: "File Management API"
  description: >-
    File Management

paths:
  /api/v1/documents:
    post:
      tags:
        - Manage Files
      summary: "Upload new file"
      operationId: "createDocument"
      requestBody:
        content:
          multipart/form-data:
            schema:
              properties:
                file:
                  type: array
                  items:
                    type: string
                    format: binary
                metadata:
                  type: object
      responses:
        201:
          description: "Document created, return generated document information"
        404:
          description: "Not Found"
        409:
          description: "Conflict"
        500:
          description: "Internal Server Error"
    get:
      operationId: "getDocument"
      responses:
        200:
          description: "return document information"
        404:
          description: "Not Found"
        409:
          description: "Conflict"
        500:
          description: "Internal Server Error"

it generate APIs as below, no "throws Exception" generated, but we really need "throws" in some cases:

default ResponseEntity<Document> createDocument(@ApiParam(value = "file detail") @Valid @RequestPart("file") MultipartFile file,@ApiParam(value = "") @RequestParam(value="metadata", required=false)  Object metadata)

default ResponseEntity<Void> getDocument()

I found two related PR/issue

1. remove "throws Exception"
   https://github.com/swagger-api/swagger-codegen/issues/7437
2. add "throws Exception" with unhandledException flag, it's global flag for all APIs
   https://github.com/OpenAPITools/openapi-generator/pull/2482

directly remove/add "throws Exception" for all APIs are not good idea, since a part of APIs need it.

Describe the solution you'd like

I think we can use Open API "Specification Extensions", with additional flag "x-" to tell generator which API need throws, which don't need.

options:

Option 1. add x-operationId-exception: true/false  ---- boolean value

api.yaml:
paths:
  /api/v1/documents:
    post:
      operationId: "createDocument"
      x-operationId-exception: true

option1.1 generate logical:

if (x-operationId-exception == true/undefined && unhandledException == true) {
   generate "throws Exception"
} else if (x-operationId-exception == false && unhandledException == true) {
   // e.g. we have 10 APIs, only a few APIs(e.g. 1,2) doesn't need throws
   no throws generated
} else if (x-operationId-exception == true && unhandledException == false/undefined) {
  // e.g. we have 10 APIs, only a few APIs(e.g. 1,2) do need throws
  generate "throws Exception"
} else if (x-operationId-exception == false/undefined && unhandledException == false/undefined) {
  no throws generated
}

option 1.2
for simple, 
if(x-operationId-exception == true)  {
  generate "throws Exception"
} else {
  no throws generated
}

Option 2. add x-operationId-exception:  ---- string array

api.yaml:
paths:
  /api/v1/documents:
    post:
      operationId: "createDocument"
      x-operationId-exception: [MyException1, MyException2]

option 2.1 generate logical:

if (x-operationId-exception is defined) {
   // no need to check unhandledException
   generate "throws MyException1, MyException2"
} else if (x-operationId-exception is undefined) {
   if (unhandledException == true) {
       generate "throws Exception"
   } else {
      no throws generated
   }
} 

option 2.2
for simple, 
if(x-operationId-exception is defined)  {
  generate "throws MyException1, MyException2"
} else {
  no throws generated
}

Option 2 (for simple, option 2.2) may be better, how do you think?

Describe alternatives you've considered

Additional context

Start by tracing how the Java generator turns an OpenAPI operation into the shown method signature and how the global unhandledException setting is handled. Compare the two proposed x-operationId-exception forms with the related issue and pull request. Done means a decided per-operation behavior, generated throws declarations matching that behavior, and coverage for operations with and without the extension.